Low molecular weight, alkali-soluble copolymers are used in inks, floor finishes, paper coatings, paints and adhesives. The copolymers are produced by bulk or solution copolymerization of a water insoluble monomer and a water soluble monomer. Acrylic acid and methacrylic acid are commonly used to introduce solubilizing functionality into such copolymers.
Emulsion polymerization offers a particularly desirable process for making such polymers because the process is free of residual solvents and the polymer produced can be solubilized directly from the emulsion by addition of base. However, the emulsion route presents a significant problem with respect to maintaining a high polymerization rate when using high levels of chain transfer agent to obtain a product having a low molecular weight.
U.S. Pat. No. 4,628,071 discloses an aqueous emulsion process for preparing a low molecular weight alkali-soluble resin from a water insoluble vinylic monomer and acrylic acid. However, substitution of methacrylic acid for acrylic acid in the method disclosed in the '071 patent is said to produce an unsatisfactory product.